1. Field of the Invention
The present invention is related to photonic devices and, in particular to integrated optical circuits.
2. Background Information
Silicon, as an electronic material, is widely used to realize electronic integrated circuits. Over ninety percent of integrated circuits fabricated worldwide use silicon as the starting material. It is well known that the highest operational frequency a silicon based electrical semiconductor device may have is limited by the speed at which the device switches. The switching speed of a bipolar semiconductor device is related to the “minority carrier life times” in the active area of the silicon crystals that makes the device work. A minority carrier is one whose equilibrium concentration (in silicon) is less than the majority carrier. For example, in N-type silicon, holes are the minority carriers and in P-type silicon, electrons are the minority carriers. The minority carrier lifetime is the average time interval between the generation and recombination of a minority carrier
The minority carrier lifetime can have a pronounced effect on the operation of a P-N junction semiconductor device because the minority carrier lifetime determines the switching response time. By introducing more recombination centers, the rate of recombination process increases. This allows the annihilation of generated/injected minority carriers within a shorter period of time, which increases the switching speed.
The number of recombination centers (or “trap centers”) in a semiconductor (e.g., silicon) is partially dependent on the presence of impurities creating energy levels inside the energy band gap. The efficiency of trap centers is characterized by capture cross-section and carriers capture rate. The most efficient traps are those having their energy levels close to the middle of band gap. Such recombination centers are called deep level recombination centers or traps.
In the mainstream silicon semiconductor industry, minority carrier lifetime modifiers for silicon are gold and platinum impurities and surface defects caused by high-energy electron irradiation. Impurities could be introduced into semiconductor by either diffusion on ion implantation.
Technologies currently exist that allow transporting of electronic data in optical form from a data source to data destination over a long distance without intermediate optical-electrical conversion. As more technologies emerge and current technologies mature, several functions previously performed in the electrical domain are migrating into optical domain functionalities.
Photonic integrated circuit fabrication technologies also are emerging and maturing. For example, among the several different planar waveguide platforms such as silica-on-silicon, lithium niobate (LiNbO3), gallium arsenide (GaAs), indium phosphide (InP), and polymer, silicon-on-insulator (SOI) is a promising substrate material for the realization of integrated optoelectronic devices, including both passive and active optical waveguide device structures.
An advantage of SOI planar waveguide platform is that the light-guiding medium is silicon, which is a semiconductor material offering very mature integrated circuit technology. Silicon is transparent in the long wavelength region (greater than 1.2 micron), which is of interest in fiber optic telecommunication. SOI already offers several benefits for scaling electronic device performance, by eliminating/reducing the substrate capacitance. In addition, with the commercially available 0.18 micron silicon complementary metal oxide semiconductor (Si CMOS) processes offered by foundry providers (e.g., TSMC in San Jose, Calif., and others), ten Gigabits per second (Gbps) lightwave circuits such as laser drivers and pre-amplifiers are possible. Furthermore, the ability to integrate germanium in silicon allows formation of long-wavelength (greater than 1.2 micron) photodetectors in silicon. Therefore, true integration of optical, electronic, and optoelectronic devices is possible on an SOI platform.